Japan's government has laid down a new set of criteria for the use of fertilizers that may be contaminated with radioactive cesium.

On Tuesday, the agriculture ministry urged farmers not to use humus and compost that contain 400 becquerels of cesium per kilogram or more.

It also called on them not to use livestock feed containing 300 becquerels of cesium per kilogram or more. For fish feed, the limit was set at 100 becquerels per kilogram.

The ministry says it will notify local governments how to measure cesium in fertilizers as soon as possible.

Last week, the agriculture ministry asked famers and fertilizer producers in 17 prefectures in eastern and central Japan to voluntarily refrain from using or selling compost and humus made from fallen leaves possibly contaminated with radioactive cesium.

This was after humus shipped from Tochigi Prefecture was found to be contaminated with radioactive substances.